Method for making moisture resistant calcium-containing particles

ABSTRACT

A method of making free-flowing moisture resistant calcium-containing particles that inhibit the water absorption characteristics of calcium products, hygroscopic and deliquescent, for example, the method comprising the steps of spraying molten soluble nitrogen-containing material onto the hygroscopic calcium-containing granules and recovering the coated granules. The core of the particle is a calcium-containing material, more particularly a soluble calcium-containing material. Moisture resistant or hydrophobic coatings are applied to the core to inhibit water absorption by the calcium-containing material. The coated particles may then be more easily shipped, stored and handled as a dry, anhydrous product. A core comprised of calcium chloride coated with urea is useful as both a soil conditioner and a fertilizer. Additional plant nutrients are mixed with either the core or the coating materials to improve fertilizing is qualities. Additional coatings of hydrophobic materials such as a paraffinic hydrocarbon or a polymeric resin increase the water resistance of the particles. A final coating of a finely divided conditioning agents such as talc or calcium carbonate can be applied to achieve a more free-flowing particle.

CROSS REFERENCE TO RELATED CASE

This is a division of U.S. patent Ser. No. 08/732,706, filed Oct. 18,1996, now U.S. Pat. No. 5,917,110.

FIELD OF THE INVENTION

The present invention relates to moisture resistant calcium-containingproducts, and more particularly to a method of making free flowingmoisture resistant calcium-containing products which are coated with oneor more materials to slow, delay, or inhibit the rate of moisture uptakeby the calcium-containing core material.

BACKGROUND OF THE INVENTION

Calcium is an ubiquitous element that occurs commonly in nature both insoluble (calcium chloride, sea water) and insoluble (gypsum, limestone)forms. It is a macronutrient essential to all life forms. Certainsoluble salts of calcium have large scale commercial significance inagriculture, road stabilization, as a soil amendment, as food additives,in the treatment of oily wastes, and as desiccants for drying gases andliquids.

Gypsum, a calcium sulfate, and limestone, a calcium carbonate, have beenused to improve soil quality, but have relatively low solubility andtherefore act slowly as soil conditioners. The soluble calcium salts,including calcium chloride which is the most prominent, presentproblems: liquid forms of these salts create bulk for shipping andstorage purposes because of their high water content (65% to 70% H₂ O).Anhydrous soluble calcium salts (90% to 95% CaCl₂), however, arehygroscopic and deliquescent, i.e. they absorb water to the point thatthe salts dissolve, creating even more long term shipping, storage andhandling problems.

The use of calcium in soil conditioning and other industries has grownsignificantly over the past decade despite these problems. Solutionscontaining calcium ions are known to greatly improve hydraulicconductivity and water infiltration rates when applied to soilscontaining clays which have been swollen by sodium absorption. Theaddition of other nutrients such as nitrogen, phosphorus, potassium,magnesium, iron, zinc, copper, manganese, molybdenum, boron and sulfur,is a good fertilization technique to improve the yield of crops.

Commercial solutions of calcium chloride and urea, the urea added toprovide nitrogen in the conditioning process, are also available.Disadvantages of these solution products include the high water contentwhich increases transportation and storage costs per unit of calcium,and the requirement that liquid application devices be used. Moreover,dry granular conditioners are more compatible with the availability ofequipment currently used in agriculture and land-use industries tospread other dry soil additives and/or fertilizers. Also, for shippingand storage purposes, anhydrous salts are obviously preferred because ofease of handling and cost effectiveness. If necessary, they may bereturned to a soluble state by mixing in water on site.

As mentioned above, the hygroscopic and deliquescent propertiesassociated with the anhydrous soluble calcium salts and some of theirhydrates create storage, handling and usage problems. Frequently,moisture is absorbed by the stored salt and converts the initiallyfree-flowing salt to a solid rock-like mass. This severely limits theshelf life, creates handling and disposal problems and generally leadsto damaged goods expenses, and sometimes total loss of product.

What is needed is a dry, granular soluble calcium-containing product inwhich the moisture-absorbing characteristics associated with thehighly-soluble calcium salts are significantly inhibited. Further, acalcium-containing material which contains a soluble calcium salt coatedwith a nitrogen containing material and/or other nutrient materialswould both inhibit moisture uptake and meet the requirements of beingcompatible with widely available spreading equipment. This simultaneousapplication of soil conditioning calcium with other requiredmacronutrients and/or micronutrients would have significant applicationto the agricultural industry. Unfortunately, admixtures of hygroscopiccalcium salts with plant nutrients do not avoid the moisture uptakeproblem. For example, calcium chloride and urea form an adduct that isat least as or even more hygroscopic than calcium chloride itself.

Prior to the present invention, the treatments available to improvecharacteristics of fertilizer or calcium containing products include (1)fertilizers or other materials coated with a hydrophobic material,usually to prevent dusting or flaking; and (2) admixtures of calciumcontaining products with additives for improved qualities, often dustcontrol.

Whittaker et al. disclose in U.S. Pat. No. 2,074,880 a molecularaddition compound of calcium sulfate and urea for use as fertilizer.Muntzer et al. in U.S. Pat. No. 3,804,661 disclose a method forproducing a solid material having hydrophobic and oleophiliccharacteristics comprising particles of chromium salt coated withparaffin used for cleaning up oil spills. U.S. Pat. No. 3,906,140 toCapes discloses co-pellets of calcium chloride and sodium chlorideformed by using binder liquid salt solutions that form bridges betweenthe initial particles upon drying. These references do not disclose theprevention of moisture absorption by coating core materials.

U.S. Pat. No. 1,592,971 to Dow discloses particles of calcium chloridein one state of hydration coated by particles of calcium chloride in alower state of hydration. Buchholz et al. in U.S. Pat. No. 5,360,465disclose particulate fertilizer dust control by treating inorganicfertilizers with a solution of urea and lignosulfate. The inorganicfertilizers include limestone and dolomite. It is noted that limestoneis a form of calcium carbonate, and dolomite is a form of a calciummagnesium carbonate. Neither are hygroscopic or deliquescent. Gleckleret al. in U.S. Pat. No. 4,252,831 disclose feed grade calcium phosphatescoated with molasses and surfactant used to minimize dusting. Buchholzand Glecker both attempted to reduce dusting.

Campbell et al. in U.S. Pat. No. 3,331,677 disclose a method ofpreparing particulate fertilizer that is coated with a urea-wax adduct.Each particle contains a core which is overlaid with a thin film whichsubstantially covers the surface of the core. The core is a dispersionof urea in paraffin wax. Both Buchholz and Campbell maximized the use ofurea in fertilizer by mixing it with additives. Campbell taught thatcoating fertilizer with a urea-wax adduct may prevent caking. Zaayengain U.S. Pat. No. 3,192,031 discloses coated fertilizer compositionscomprised of urea coated with a first coating of diatomaceous earth anda second coating of wax.

Buhler et al. in U.S. Pat. No. 3,740,248 disclose starch particlescoated with wax to prevent offset of print from freshly printed sheets.Dubois in U.S. Pat. No. 4,012,537 discloses de-icing compositionscontained in asphalt road surface material comprised of calcium orsodium chloride coated with linseed oil or other water-tight coatingthat may be worn away by mechanical action such as traffic movement.

None of these references, however, teach or suggest a core of acalcium-containing material which is hygroscopic or deliquescentcombined with a less hygroscopic, soluble non-calcium coating materialto inhibit the uptake of moisture by the core material.

SUMMARY OF THE INVENTION

The present invention resides, in part, in the discovery that particlesof soluble calcium-containing materials can be coated with anothermaterial which is also soluble, but nonetheless inhibits moisture uptakeby the calcium-containing material. This makes possible all sorts ofapplications where the coating material and the calcium-containingmaterial are both useful in the desired application. As one example,particles comprising a calcium chloride core and a soluble nitrogenfertilizer coating such as urea, can be stored, shipped and applied as afree-flowing solid with better resistance to moisture than the calciumchloride without the coating.

Broadly, the free-flowing moisture-resistant calcium-containingparticles made by the present invention comprise a core of hygroscopiccalcium-containing material and an essentially calcium-free solublecoating on an outer surface of the core to inhibit moisture uptake bythe core. The core can include an ammonia based material. Preferably,the moisture-resistant calcium-containing particles can include ahydrophobic coating over the soluble coating, or the soluble coating caninclude a hydrophobic material.

Another aspect of this method for making free-flowing moisture-resistantcalcium-containing particles comprises the steps of 1) spraying a moltensoluble nitrogen-containing material onto hygroscopic calcium-containinggranules sufficiently cool to solidify the molten material into amoisture-inhibiting coating on the particles, and 2) recovering thecoated granules. Another step in this method can include applying ahydrophobic coating over the nitrogen-containing material.Alternatively, the nitrogen-containing material can include ahydrophobic material. The coated granules can be admixed with a finelydivided conditioning agent. Another aspect of this invention is a methodof making a a soil amendment.

In the above-described method, the calcium-containing granules can beselected from a group consisting of calcium chloride, calcium nitrate,calcium formate, calcium acetate, a calcium salt of another organicacid, a calcium saccharide compound, or a combination thereof.Preferably, the nitrogen-containing material is selected from the groupconsisting of urea, ammonium nitrate, urea phosphate melamine, ureaaldehyde polymers, monoammonium phosphate, diammonium phosphate or acombination thereof. The hydrophobic coating can comprise a paraffinichydrocarbon, preferably, petrolatum with a melting point between 100° F.and 260° F. The calcium-containing particles can have a water contentless than 50 weight percent.

The calcium-containing particles preferably include one or more plantnutrients. The plant nutrients are selected from the group consisting ofphosphorus, potassium, magnesium, iron, copper, zinc, manganese,molybdenum, sulfur, boron and combinations thereof. In the preferredmethod, the spraying step is effected in a rotating pan or drum.

In another aspect of the method for making free-flowing calcium chlorideparticles, the steps are 1) spraying a molten solublenitrogen-containing material onto calcium chloride granules sufficientlycool to solidify the molten material into a moisture-inhibiting coatingon the granules; and 2) recovering the coated granules. In a preferredmethod the coated particles have a particle size distributionsubstantially between 0.4 and 5 mm. The calcium chloride particles canhave a water content of less than 50 weight percent. Preferably, from 5to 35 parts by weight of the nitrogen-containing compound is sprayed on100 parts by weight calcium chloride including any water of hydration.Preferably, there is a further step of applying an outer coating of from1 to 15 weight percent petrolatum. More preferably, there is a stillfurther step of admixing the coated particles with a finely-dividedconditioning agent.

Preferably, the calcium chloride particle or the nitrogen-containingmaterial can contain another plant nutrient. In a preferred embodimentof this method, the nitrogen-containing material is urea. In anotheraspect of this method there is a further step of spraying formaldehydeon the urea-coated particles to form an outer layer of urea-formaldehyderesin. Preferably, the molten urea is sprayed at a temperature of about280° F., and the recovered coated particles have a temperature less than120° F. The free-flowing calcium chloride granules can then be appliedto the soil.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The free-flowing moisture resistant calcium-containing particles of thisinvention inhibit the water absorption characteristics of calciumproducts, including soluble calcium products that are hygroscopic anddeliquescent. According to the teachings of this invention, a core of acalcium containing material can have one or more coatings that aremoisture resistant or even hydrophobic to inhibit water absorption. Thecoated particles may then be shipped, stored and handled as a dry,anhydrous product with less risk of problems caused by exposure tohumidity.

In the agricultural industry, the core is preferably calcium chloride.If coated as disclosed in this invention with urea or other nitrogensources, it is useful as both a soil conditioner and a fertilizer. Itcan be even more useful if other plant nutrients are mixed with eitherthe core or the coating materials of the particles. Additional coatingsof hydrophobic materials increase the water resistance of the particles.Mixing with a finely divided conditioning agent such as talc or calciumcarbonate can be effected to achieve a more free-flowing particle.

Although the significance of moisture resistant calcium-containingproducts is important in the agricultural and land use industies, thecomposition and method of producing the free-flowing moisture resistantcalcium-containing particles of this invention can be useful in anyindustry that requires calcium salts, such as, for example, in the foodindustry, as a compacting agent in road stabilization, road de-icing, inthe treatment of oily wastes and as a desiccant for drying gases andliquids. The core can comprise soluble calcium salts including calciumchloride, calcium nitrate, calcium formate, calcium acetate, a calciumsalt of another organic acid, a calcium saccharide compound, or acombination thereof. For the purposes of illustration and simplicity,the invention will be described below with reference to calcium chlorideas a preferred example, but it is understood that the present inventionis not limited to calcium chloride as the core material.

The calcium chloride core preferably has a water content of less than50% weight percent. More preferred is a granular chloride having 75 to95 weight percent, preferrably, 94 weight percent CaCl₂. When thecalcium-containing core is calcium nitrate, it preferably has less than30 weight percent combined moisture. When the calcium-containing core iscalcium acetate, it should contain less than 19 weight percent combinedmoisture.

When used as a soil amendment, soil conditioner or fertilizer, thecalcium-containing core can include one or more other plant nutrients.These plant macro- or micro-nutrients are selected from the groupconsisting of phosphorus, potassium, magnesium, iron, copper, zinc,manganese, molybdenum, sulfur, boron and combinations thereof. Thesenutrients are present as salts or in other forms in which the nutrientelement can be released into the soil or other plant growth media.

When used as a soil conditioner or fertilizer, this compositioncomprises particles having a calcium chloride core, with or withoutadditional plant nutrients, and an essentially calcium-free solublenitrogen-containing coating which may also contain an additional plantnutrient, wherein the coating inhibits moisture uptake by the core. Thenitrogen-containing coating is preferably urea, ammonium nitrate, ureaphosphate, melamine, urea aldehyde polymers, monoammonium phosphate,diammonium phosphate, or the like or a combination of the above. Thecalcium-containing core can also include an ammonia-based material, forexample, ammonium sulfate, ammonium nitrate or ammonium chloride, or thelike.

Preferably, the free-flowing, urea-coated calcium chloride particleshave from 5 to 35 parts by weight urea, per 100 parts by weight calciumchloride including any water of hydration.

The moisture-resistant calcium-containing particles can also have asecond coating of a hydrophobic material over the first soluble coating.The hydrophobic coating can be a paraffinic hydrocarbon such aspetrolatum or paraffin with a melting point between 100° F. and 260° F.In a more preferred embodiment, the free-flowing particles have an outercoating of from 1 to 15 weight percent petrolatum. Alternatively, thehydrophobic coating can be a polymeric resin material, such as, forexample, urea-formaldehyde, polyethylene, polypropylene, polystyrene, orthe like. As another alternative, the hydrophobic material is dispersedin the soluble coating.

If desired, the calcium chloride particle can have an intermediate layerbetween the nitrogen-containing or other soluble coating and theunderlying core. The intermediate layer can be formed, for example, asthe reaction product of the soluble coating and the calcium chloride,e.g. calcium chloride-urea adduct. Alternatively, the intermediate layercan be the reaction product of calcium chloride with a material such as,for example, sulfate, phosphate, silicate, or the like which forms aninsoluble calcium compound. In this manner, moisture uptake is inhibitedby the newly formed calcium-containing materials and the remainingunaltered calcium-containing core material can slowly release calciumover a longer period of time. As another alternative, the hydrophobicmaterial mentioned above can also be used as an intermediate layer.

In addition, the coated, moisture-resistant calcium-containing particlescan be in an admixture with a finely divided conditioning agent.Suitable conditioning agents are, for example, talc, calcium carbonate,calcium hydroxide, calcium oxide, apatite, dolomite, diatomaceous earth,perlite, volcanic glasses, bentonite, montmorillonite, kaolin,vermiculite, attapulgite or the like. The conditioning agents keep theparticles from sticking together and promote slip to keep the particlesin a free-flowing state.

The resulting moisture-resistant calcium-containing particles preferablyhave a particle size distribution substantially between 0.4 and 5 mm.For most agricultural applications, a particle size of less than 3 mm ismore preferred. However, in various land use applications such as thoseused in modern forestry, particle size can increase up to 3 inches indiameter. These large-size particles can be used for air dropfertilization and soil conditioning over large land area where thelarger sized particles are necessary to get through dense vegetation.

In agriculture, particle size is important in soil conditioners andfertilizers because of standardized spreading equipment and the commonpractice of blending various dry soil additives so that only oneapplication is required. It is generally accepted that bulk, dryfertilizers and soil additives have a size range between 6 mesh U.S.Standard (3.35 mm) and 16 mesh U.S. Standard (1.19 mm). The particlesize distribution is frequently characterized by a Size Guide Number,SGN, which is defined as the size at which 50% is retained, expressed inmillimeters multiplied by 100 and rounded to the nearest 5. Many dry,granular materials have SGN's between 190 and 230. Desirably, theparticle size distribution is relatively narrow.

The moisture-resistant calcium-containing products are generally made byapplying a coating of the desired coating material. In a preferredmethod, the dry, granular calcium salt is fed into a coating device suchas a drum granulator, drum coater, pan or disk granulator, pan or diskcoater, a fluid bed granulator or coater or any other suitable devicedesigned for coating. Preferred apparatus for granulation and coating ofmaterials are described in the following patents to Shirley, Jr. et al.:U.S. Pat. No. 4,213,924, U.S. Pat. No. 4,424,176, and U.S. Pat. No.4,506,453 which are hereby incorporated herein by reference in theirentirety as if fully reproduced.

Briefly, a rotary drum coater, is inclined at an angle from about 0degrees to about 10 degrees from the horizontal. The amount ofinclination depends on the desired residence time and other operatingparameters. The size of the drum is determined by the desiredthroughput. The coating agent in liquid form is introduced into thecoating device through a system of spray nozzles.

A preferred first coating agent is molten urea (46.6% nitrogen, m.p.274° F./134° C.), but other materials such as molten ammonium nitrate,urea-water solutions, ammonium nitrate-water solutions, are alsoconsidered to be part of this invention. For the purposes ofillustration and simplicity, the invention will be described below withreference to molten urea as a preferred example, but it is understoodthat the present invention is not limited to molten urea as the coatingmaterial.

The first coating apparatus should provide sufficient residence time, toallow the calcium salt core granules to be evenly coated, for example,0.5 to 60 minutes. If desired, the coated calcium core can then bepassed to a separate cooling or drying apparatus such as a drum or afluid bed, preferably a rotary drum. The rotary drum dries or cools thecoated core to a temperature below the melting point of the coating, sothat the coated particles are no longer sticky. Where molten urea isused as a coating material, particles discharged from the rotary coatingdrum (or separate cooler if used) have a temperature below the meltingpoint of urea, preferably below 120° F. Other molten coatings requiredifferent discharge temperatures. For aqueous or other solvent coatingmaterials, the apparatus can serve as a dryer to remove water or othersolvents by having heated air introduced at the discharge point or atthe feed point.

A precoating material is optionally applied to the calcium salt corebefore the application of the urea coating by the previously describedmethod so that an intermediate layer is formed between the calcium saltcore and the urea coating. A precoating of a hydrophobic material,polymer or an insoluble sulfate, phosphate or silicate can increase themoisture resistant qualities of the particles.

Preferably, a hydrophobic coating is applied to the urea-coatedcalcium-containing particle by adding the hydrophobic material at theexit end of drum. Alternatively, the coated particles can be passedthrough another coating apparatus suitable for coating as describedabove, for example, a drum granulator, drum coater, pan or diskgranulator, pan or disk coater, a fluid bed granulator or coater or thelike. The hydrophobic coating can be in a molten form or alternativelyapplied as an aqueous or solvent solution of a polymer orpolymer-forming material, such as, for example, a solution offormaldehyde in water with or without methanol stabilization, a solutionof amine-formaldehyde, molten sulfur, any of the aliphatic or polyolpolymers such as polyethylene, polyethylene glycol, polyvinyl alcohol orthe like.

If desired, the hydrophobic coated particle is then passed to a coolingor drying apparatus such as drum cooler/dryer or a fluid bedcooler/dryer, preferably a rotary drum cooler/dryer. Molten coatingsrequire cooling to a temperature below the melting point so that thedischarged solid particles are not sticky. Aqueous or other solventsolutions are dried to remove the water or other solvent and cure anyresins formed during the process.

A preferred final step in the method of making the moisture-resistantcalcium containing particles is conditioning the coated particle byadmixing it with one of the conditioning agents mentioned above usingconventional solids blending equipment and procedures.

The additional plant nutrients mentioned above can also be appliedeither prior to or simultaneously with the precoating or coatingmaterials, e.g. by blending with the molten urea prior to the sprayingstep. The plant nutrients can additionally or alternatively beincorporated into the calcium core, any precoating material, thehydrophobic coating, and/or the conditioning agents in the desiredproportion. Alternatively, the additional nutrient can be applied as aseparate coating under or over the urea coating.

The preferred method of making moisture-resistant calcium containingparticles includes a step of passing the particles through a screeningapparatus where the coated particles are classified into oversized,onsize, or undersized fractions. The inappropriate sized products may berecycled or further treated.

As used in the land use and agricultural industies, the free-flowing,coated particles of this invention can be applied independently as asoil amendment or fertilizer.

The present invention is further illustrated by the following examples.

EXAMPLES Example 1

A commercial brand of granular, anhydrous calcium chloride (94% CaCl₂)was fed at a rate of 90.5 lbs/hour onto a rotating pan. Molten urea wassprayed from a full cone nozzle, positioned 6 inches above the rotatingbed of calcium chloride. The temperature of the molten urea wasmaintained at 140° C. (284° F.) with a heated urea melting system. Therate of urea application was 24.5 lbs/hour. A red dye was added to themolten urea so that the effectiveness of the coating of the calciumchloride could be visually observed. Visual inspection indicated thatapproximately 80-85% of the calcium chloride fed to the pan granulatorwas well coated. The total rate of production of urea-coated calciumchloride was 115 lbs/hour. The hot coated product from the pan wastransferred into containers by a conveyor and cooled. The productcontained 26.7 weight percent calcium (74.0 weight percent calciumchloride), 9.9 weight percent nitrogen (21.4 weight percent urea) and4.6 weight percent water.

Example 2

A commercial brand of granular, anhydrous calcium chloride (94% CaCl₂)was fed at a rate of 270 lbs/hour onto a rotating pan. Molten urea wassprayed from nozzles, positioned above the rotating bed of calciumchloride. The temperature of the molten urea was maintained at 140° C.(284° F.) with a heated urea melting system. A green dye was added tothe urea so that the extent of urea coverage of the calcium chloridecould be monitored. The rate of urea application was 23.4 lbs/hour andthe rate of production of the urea-coated calcium chloride was 293.4lbs/hour. The hot coated product from the pan granulator was transferredinto containers by a conveyor and cooled. It appeared that approximately90% of the calcium chloride fed to the pan granulator was well coated.This first product contained 31.2 weight percent calcium (86.5 weightpercent calcium chloride), 3.73 weight percent nitrogen (8.0 weightpercent urea) and 5.50 weight percent water.

To simulate a second stage of coating, this first product wasreintroduced to the rotating pan at a feed rate of 270 lbs/hour, andsprayed a second time with molten urea. The urea rate in this secondapplication was 30 lbs/hour. This second product was conveyed to storagebins and cooled. This twice-coated product contained 28.2 weight percentcalcium (78.0 weight percent calcium chloride), 7.9 weight percentnitrogen (17.0 weight percent urea) and 5.0 weight percent water.

The rates of moisture uptake by the first product containing 8.0 weightpercent urea, by the second product containing 17.0 weight percent ureaand by untreated calcium chloride were measured at 24° C. and 45%relative humidity. The data in Table 1 below show that the rate ofmoisture uptake decreases as the weight percent of urea in the coatingincreases.

                  TABLE 1                                                         ______________________________________                                        Uncoated CaCl.sub.2                                                           Time         Grams Moisture/                                                  (Minutes)    Gram Sample                                                      ______________________________________                                        0.0          0.000                                                            27.0         0.052                                                            28.0         0.058                                                            39.0         0.091                                                            54.0         0.119                                                            67.0         0.103                                                            68.0         0.114                                                            96.0         0.169                                                            97.0         0.172                                                            114.0        0.211                                                            ______________________________________                                        CaCl.sub.2 Coated with 8% Urea                                                Time         Grams Moisture/                                                  (Minutes)    Gram Sample                                                      ______________________________________                                        0.0          0.000                                                            17.1         0.034                                                            58.1         0.090                                                            78.1         0.114                                                            110.1        0.1                                                              138.1        0.182                                                            ______________________________________                                        CaCl.sub.2 Coated with 17% Urea                                               Time         Grams Moisture/                                                  (Minutes)    Gram Sample                                                      ______________________________________                                        0.0          0.000                                                            18.7         0.022                                                            59.7         0.065                                                            79.9         0.086                                                            111.0        0.125                                                            139.2        0.176                                                            ______________________________________                                         R.H. = 45%                                                                    Temp. = 24° C.                                                    

Example 3

A commercial brand of granular, anhydrous calcium chloride (94% CaCl₂)was fed at a rate of 270 lbs/hour onto a rotating pan. Molten urea wassprayed from nozzles, positioned above the rotating bed of calciumchloride. The temperature of the molten urea was maintained at 140° C.(284° F.) with a heated urea melting system. The rate of ureaapplication was 47.6 lbs/hour and the rate of production of theurea-coated calcium chloride was 317.6 lbs/hour.

The experiment was repeated a second time. The only difference was that1.0% formaldehyde in the form of a commercially availableurea-formaldehyde resin was added to the molten urea. In bothexperiments the urea content of the product was approximately 15%.

The rates of moisture uptake by the products from the two experimentswere measured at 20° C. and 47% relative humidity. The data in Table 2below show that the addition of formaldehyde to the product decreasedthe rate of moisture uptake to a small extent.

                  TABLE 2                                                         ______________________________________                                                         CaCl.sub.2 Coated with 15% Urea                              CaCl.sub.2 Coated with 15% Urea                                                                and 1% Formaledhyde                                          Time     Grams Moisture/                                                                           Time        Grams Moisture/                              (Minutes)                                                                              Gram Sample (Minutes)   Gram Sample                                  ______________________________________                                        0.0      0.000       0.0         0.000                                        12.5     0.017       12.2        0.012                                        23.4     0.030       23.4        0.023                                        37.3     0.047       41.5        0.042                                        59.5     0.069       59.6        0.055                                        80.8     0.092       71.8        0.075                                        113.9    0.124       90.2        0.083                                                             101.5       0.091                                                             120.3       0.102                                        ______________________________________                                         R.H. = 47%                                                                    Temp. = 20° C.                                                    

Example 4

A commercial brand of granular, anhydrous calcium chloride (94 weightpercent CaCl₂) was introduced into a rotating coating drum at a rate of317 lbs/hour. Molten urea containing a red dye was sprayed on thefalling particles. The rate of urea addition was 79.6 lbs/hour. Theproduct leaving the drum was conveyed to bins and cooled. The productcontained 27 weight percent calcium (75.2 weight percent calciumchloride), 9.3 weight percent nitrogen (20 weight percent urea) and 4.8weight percent water. Visual observation indicated that 90-95% of theproduct granules were well coated. The rate of moisture uptake wasmeasured at a relative humidity of 43% and a temperature of 23° C. Table3 compares the observed moisture uptake rate to that of untreatedcalcium chloride. Clearly the rate of moisture uptake has beensignificantly decreased by the 20 weight percent coating of urea.

                  TABLE 3                                                         ______________________________________                                        Uncoated CaCl.sub.2                                                                            CaCl.sub.2 Coated with 20% Urea                              Time     Grams Moisture/                                                                           Time        Grams Moisture/                              (Minutes)                                                                              Gram Sample (Minutes)   Gram Sample                                  ______________________________________                                        0.0      0.000       0.0         0.000                                        27.5     0.055       19.3        0.008                                        39.0     0.091       38.3        0.016                                        54.0     0.119       61.7        0.024                                        67.5     0.109       97.7        0.038                                        96.5     0.142       161.3       0.062                                        114.0    0.211       225.3       0.085                                        166.5    0.212       344.2       0.119                                        188.0    0.300       439.7       0.146                                        231.0    0.307                                                                269.0    0.368                                                                282.0    0.380                                                                317.0    0.428                                                                353.0    0.476                                                                378.0    0.511                                                                ______________________________________                                         R.H. = 43%                                                                    Temp. = 23° C.                                                    

The particle size distributions of the coated and uncoated calciumchloride were determined by dry screening. The untreated calciumchloride prior to coating had a Size Guide Number (SGN) of 125, and theurea-coated particles had a SGN of 210. At the same time, the proportionof fines passing through the 16 and 20 mesh screens was substantiallyreduced after coating with urea, indicating that the particle sizedistribution was much narrower.

Example 5

A commercial brand of granular, anhydrous calcium chloride (94 wt %CaCl₂), with a particle size range between 6 mesh U.S. Standard (3.35mm) and 16 mesh U.S. Standard (1.19 mm) was introduced into a rotatingcoating drum at a rate of about 480 lbs/hour. Molten urea containing agreen dye was sprayed at a rate of about 120 lbs/hour on the fallingparticles and the bed of particles in the drum. After achieving asteady, consistent operation, samples of the coated calcium chloride,being produced at 600 lbs/hour, were taken for analysis and evaluation.Visual observation indicated that over 95% of the product granules werewell coated. Then a flow of melted petrolatum was started and added tothe already coated materials at the exit end of the coating drum. Onexiting the drum this material was fed to a small conditioning drum,where dry, powdered talc was added at about 24 lbs/hour. After achievinga steady, consistent operation, samples of the free-flowing coated andconditioned material were taken for analysis and evaluation. The samplesof coated material which did not have any petrolatum contained 10.1 wt %nitrogen (21.7 wt % urea), 26.5 wt % calcium (73.9 wt % calciumchloride) and 4.4 wt % water. The samples of coated material which hadthe petrolatum and conditioning agents added contained 9.3 wt % nitrogen(19.0 wt % urea) and 25.2 wt % calcium (70.5 wt % calcium chloride).Moisture uptake measurements were made on both samples. The results areshown in Table 4. The addition of the petrolatum reduced the rate ofmoisture uptake significantly compared to that of urea alone.

                  TABLE 4                                                         ______________________________________                                                         CaCl.sub.2 Coated with 20% Urea,                             Coated with 20% Urea                                                                           2% Petrolatum, 3.5% Talc                                     Time     Grams Moisture/                                                                           Time        Grams Moisture/                              (Minutes)                                                                              Gram Sample (Minutes)   Gram Sample                                  ______________________________________                                        0.0      0.000       0.0         0.000                                        13.0     0.008       10.0        0.001                                        39.0     0.022       11.0        0.001                                        60.0     0.032       24.0        0.001                                        102.0    0.055       31.0        0.001                                        193.0    0.104       43.0        0.002                                        60.0     0.003                                                                63.0     0.003                                                                87.0     0.004                                                                121.0    0.006                                                                144.0    0.009                                                                212.0    0.012                                                                266.0    0.013                                                                462.0    0.023                                                                ______________________________________                                         R.H. = 52.6%                                                                  Temp. = 24.3° C.                                                  

The foregoing description is illustrative and explanatory of preferredembodiments of the invention, and variations in the size, shape,materials and other details will become apparent to those skilled in theart. It is intended that all such variations and modifications whichfall within the scope or spirit of the appended claims be embracedthereby.

I claim:
 1. A method for making free-flowing moisture resistant,calcium-containing particles, comprising:spraying a molten solublenitrogen-containing material onto hygroscopic calcium-containinggranules which are sufficiently cool to solidify the molten materialinto a moisture-inhibiting coating on the granules; and recovering thecoated granules.
 2. The method of claim 1 further comprising applying ahydrophobic coating over the nitrogen-containing material.
 3. The methodof claim 1 wherein the nitrogen-containing material includes ahydrophobic material.
 4. The method of claim 2 further comprisingadmixing the coated particles with a finely divided conditioning agent.5. The method of claim 3 further comprising admixing the coatedparticles with a finely divided conditioning agent.
 6. The method ofclaim 1 wherein the calcium-containing granules are selected from thegroup consisting of calcium chloride, calcium nitrate, calcium formate,calcium acetate, a calcium salt of another organic acid, a calciumsaccharide compound, and combinations thereof.
 7. The method of claim 1wherein the nitrogen-containing material is selected from the groupconsisting of urea, ammonium nitrate, urea phosphate, melamine, ureaaldehyde polymers, monoammonium phosphate, diammonium phosphate, andcombinations thereof.
 8. The method of claim 2 wherein the hydrophobiccoating comprises a paraffinic hydrocarbon.
 9. The method of claim 8wherein the paraffinic hydrocarbon is petrolatum with a melting pointbetween 100° F. and 260° F.
 10. The method of claim 3 wherein thehydrophobic material comprises a paraffinic hydrocarbon.
 11. The methodof claim 1 wherein the calcium-containing particles include one or moreplant nutrients.
 12. The method of claim 11 wherein the plant nutrientsare selected from the group consisting of phosphorus, potassium,magnesium, iron, copper, zinc, manganese, molybdenum, sulfur, boron andcombinations thereof.
 13. The method of claim 1 wherein the sprayingstep is effected in a rotating pan or drum.
 14. The method of claim 1wherein the calcium-containing granules have a water content less than50 weight percent.
 15. A method for making free-flowing calcium chlorideparticles, comprising the steps of:spraying a molten solublenitrogen-containing material onto calcium chloride granules sufficientlycool to solidify the molten material into a moisture-inhibiting coatingon the granules; and recovering the coated granules.
 16. The method ofclaim 15 wherein the coated granules have a size distributionsubstantially between 0.4 and 5 mm.
 17. The method of claim 15 whereinthe calcium chloride granules have a water content less than 50 weightpercent.
 18. The method of claim 15 wherein from 5 to 35 parts by weightof the nitrogen-containing compound is sprayed on 100 parts by weightcalcium chloride including any water or hydration.
 19. The method ofclaim 15 comprising the further step of applying an outer coating ofhydrophobic material.
 20. The method of claim 19 wherein the hydrophobicmaterial comprises petrolatum with a melting point between 100° F. and260° F.
 21. The method of claim 20 comprising the further step ofadmixing the coated particles with a finely-divided conditioning agent.22. The method of claim 15 wherein the calcium chloride granule or thenitrogen-containing material contains a plant nutrient.
 23. The methodof claim 15 wherein the nitrogen-containing material is urea.
 24. Themethod of claim 23 comprising the further step of spraying formaldehydeon the urea-coated particles to form an outer layer of urea-formaldehyderesin.
 25. The method of claim 23 wherein the molten urea is sprayed ata temperature of about 280° F.
 26. The method of claim 25 wherein therecovered coated particles have a temperature less than 120° F.
 27. Themethod of claim 15 further comprising applying the free-flowing calciumchloride particles to soil.